Epitaxial Ag island - GeSi(100) quantum dot nanocomposites for Si-based light emission

Project: Research project

Description

This project seeks to endow Si-compatible materials with increased optical functionality. Epitaxial architectures that arrange Ag islands in proximity to Ge/Si(100) quantum dots (QDs) will be investigated to assess plasmonic enhancements to luminescence efficiency. The localized surface plasmon (LSP) mode of the Ag island is predicted to improve both the absorption and emission of photons by the Ge QD. Increased absorption results from the dramatic field concentration near the Ag nanoparticle. The Purcell effect increases the spontaneous emission rate. Recent theoretical work suggests that plasmonic enhancements will be greatest for optimally arranged Ge dots and Ag islands if the LSP resonance frequency is close to that of the QD exciton. The near UV LSP resonance of the Ag islands will be tuned to match the near IR exciton energy of the Ge/Si(100) QDs using a combination of shape resonance effects and by varying their dielectric environment. In the ideal case, theory predicts the luminescence enhancement can approach two orders of magnitude. A variety of strategies for templating Ag/Si(100) island growth atop Si-encapsulated Ge dots will be investigated in order to identify the one that is most effective. These strategies rely on defining the fundamental material science of Ag/Si(100) island growth that, surprisingly, is not well understood. One focus will be to determine whether the inhomogeneously strained planar surface of the Si layer that caps the buried Ge dots can affect the thermodynamics or kinetics of Ag island nucleation. The second focus will be on the nm-scale pits found immediately above the Ge dots just prior to completion of the Si cap layer. These pits will be investigated for their potential as inhomogeneous nucleation sites for Ag islands. Finally, the surface topography of periodically pitpatterned Si substrates that template Ge dot growth will also be investigated to assess their efficacy for proximally locating the Ag islands. This final strategy also offers the opportunity for exploiting collective plasmonic grating effects when the decay length of the Ag LSP fields are longer than the pattern periodicity. Various dielectric layers will be deposited atop the epitaxial Ag islands in order to redshift their LSP resonance closer to the Ge QD exciton energy. Simple estimates indicate that higher dielectric constants yield larger redshifts. Si (.. = 11.9) is particularly attractive and easy to grow so it will be investigated first. The extinction characteristics of the Ag island/Ge QD nanocomposites will be assessed using UV/VIS spectroscopy and correlated with luminescence enhancements measured using standard photoluminescence (PL) spectroscopy. PL will be excited at several wavelengths throughout the visible into the near IR in order to investigate theoretically predicted excitation detuning effects on luminescence efficiency. Ge/Si(100) QDs luminesce at the 1.5..m low-loss transmission wavelength in optical fibers. Their low efficiency has precluded wide-ranging application. Plasmonically enhancing their luminescence could have enormous technological impact, enabling Si-based optoelectronics, and could leverage the enormous investment in Si CMOS logic devices. In addition to the fundamental science gained and potential for technological and economic impact, this project will positively affect the education and future career of the student(s) involved in the research. They will be trained in the synthesis as well as the structural and optical characterization of materials and architectures in the rapidly growing field of plasmonics. Additionally, links to the highly successful Science is Fun program offered by the Leroy Eyring Center for Solid State Science at ASU will be established. This program impacts on average 12,000 high and middle school students annually. The PI will work closely with Science is Fun staff and interns to develop hands-on, age-appropriat
StatusFinished
Effective start/end date7/1/106/30/15

Funding

  • National Science Foundation (NSF): $443,746.00

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light emission
nanocomposites
quantum dots
luminescence
surface plasmon resonance
augmentation
excitons
caps
students
economic impact
nucleation
photoluminescence
transmission loss
materials science
wavelengths
spontaneous emission
spectroscopy
logic
proximity
periodic variations